Multiple channel-electrode mapping

ABSTRACT

In accordance with one aspect of the invention, methods and systems are disclosed for delivering a stimulating signal by a stimulating medical device having a plurality of electrodes. Such methods and systems comprise receiving a signal; filtering the received signal to obtain a plurality of band pass filtered signals; delivering to each electrode of a first group of one or more electrodes, a first set of stimulation signals, wherein the first set of stimulation signals comprises stimulations signals for each of a first group of two or more band pass filtered signals; and delivering to each of electrodes of a second group of one or more electrodes, a second set of stimulation signals, wherein the second set of stimulation signals comprises stimulations signals for each of a second group of one or more band pass filtered signals; and wherein the first set of stimulation signals are delivered at a different effective stimulation rate than the second set of stimulation signals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/192,014, entitled “Variable Width Electrode Scheme,” filedJul. 29, 2005. This application also claims the benefit of U.S.Provisional Application No. 60/607,363, filed Sep. 7, 2004. The entiredisclosure and contents of the above applications are herebyincorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to a stimulating medical deviceand, more particularly, to multi-channel stimulation of a medicaldevice.

2. Related Art

Delivery of electrical stimulation to appropriate locations within arecipient or patient (referred to herein as a recipient) may be used fora variety of purposes. For example, function electrical stimulation(FES) systems may be used to deliver electrical pulses to certainmuscles of a recipient to cause a controlled movement of a limb of therecipient.

As another example, a prosthetic hearing implant system may be used todirectly deliver electrical stimulation to auditory nerve fibers of arecipient's cochlea to cause the recipient's brain to perceive a hearingsensation resembling the natural hearing sensation normally delivered tothe auditory nerve.

Prosthetic hearing implant systems typically have two primarycomponents: an external component commonly referred to as a speechprocessor, and an implanted component commonly referred to as areceiver/stimulator unit. Traditionally, both of these componentscooperate with each other to provide sound sensations to a recipient.

The external component traditionally includes a microphone that detectssounds, such as speech and environmental sounds, a speech processor thatselects and converts certain detected sounds, particularly speech, intoa coded signal, a power source such is a battery, and an externaltransmitter antenna.

The coded signal output by the speech processor is transmittedtranscutaneously to the implanted receiver/stimulator unit, commonlylocated within a recess of the temporal bone of the recipient. Thistranscutaneous transmission occurs via the external transmitter antennawhich is positioned to communicate with an implanted receiver antennadisposed within the receiver/stimulator unit. This communicationtransmits the coded sound signal while also providing power to theimplanted receiver/stimulator unit. Conventionally, this link has beenin the form of a radio frequency (RF) link, but other communication andpower links have been proposed and implemented with varying degrees ofsuccess.

The implanted receiver/stimulator unit traditionally includes the notedreceiver antenna that receives the coded signal and power from theexternal component. The implanted unit also includes a stimulator thatprocesses the coded signal and outputs an electrical stimulation signalto an intra-cochlea electrode assembly mounted to a carrier member. Theelectrode assembly typically has a plurality of electrodes that applythe electrical stimulation directly to the auditory nerve to produce ahearing sensation corresponding to the original detected sound.

In the conversion of sound to electrical stimulation by the speechprocessor, it is common in the prosthetic hearing implant field toallocate frequencies from a filter bank or similar frequency analyzer toindividual electrodes of the electrode assembly. This “mapping” istypically done on a one-to-one basis, that is, each filter output isallocated to a single electrode. It is typical to allocate frequenciesto electrodes that lie in positions in the cochlea that are close to theregion that would naturally be stimulated in normal hearing. However,signal processing techniques implemented in conventional prosthetichearing devices often fail to map to the optimal electrodes in thecochlea, thus limiting their ability to provide the desired perceptionof hearing.

SUMMARY

According to one aspect of the invention, methods and systems areprovided for delivering a stimulating signal by a stimulating medicaldevice having a plurality of electrodes. Such methods and systemscomprise receiving a signal; filtering the received signal to obtain aplurality of band pass filtered signals; delivering to each electrode ofa first group of one or more electrodes, a first set of stimulationsignals, wherein the first set of stimulation signals comprisesstimulations signals for each of a first group of two or more band passfiltered signals; and delivering to each of electrodes of a second groupof one or more electrodes, a second set of stimulation signals, whereinthe second set of stimulation signals comprises stimulations signals foreach of a second group of one or more band pass filtered signals; andwherein the first set of stimulation signals are delivered at adifferent effective stimulation rate than the second set of stimulationsignals

According to another aspect, methods and systems are provided for acochlear implant system, comprising a plurality of electrodes disposedin a cochlear of a recipient, wherein the plurality of electrodescomprise a first group of one or more electrodes and a second group ofone or more electrodes, a speech processor, and a stimulator unit.According to an aspect, the speech processor comprises a plurality ofband pass filters configured to process received acoustical signals toobtain a plurality of band pass filtered signals. Further, in an aspect,the stimulator unit is configured to deliver to each electrode of afirst group of one or more electrodes, a first set of stimulationsignals, wherein the first set of stimulation signals comprisesstimulations signals for each of a first group of two or more band passfiltered signals, and to deliver to a second group of one or moreelectrodes a second set of stimulation signals, wherein the second setof stimulation signals comprises stimulations signals for each of asecond group of one or more band pass filtered signals, and wherein thefirst set of stimulation signals are delivered at a different effectivestimulation rate than the second set of stimulation signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary hearing implant systemsuitable for implementing embodiments of the present invention;

FIG. 2 illustrates a simplified functional block diagram of a hearingimplant system in accordance with one embodiment of the presentinvention;

FIG. 3 illustrates a more detailed diagram of logical blocks of FIG. 2;

FIG. 4 depicts a table that illustrates an exemplary mapping forimplementing an MEM strategy in which multiple filter channels aremapped to a single group of one or more electrodes;

FIG. 5 illustrates a table that provides an exemplary stimulus timingsequence for a simple stimulation strategy;

FIG. 6 illustrates a table that provides an alternative channel timingsequence for a stimuation strategy;

FIG. 7 illustrates filter bands for an exemplary SCF band pass filterbank

FIG. 8A illustrates exemplary filter bands for the SCF band pass filterbank of FIG. 7, where the filter clock frequency has been decreased;

FIG. 8B illustrates exemplary filter bands for the SCF band pass filterbank of FIG. 7, where the filter clock frequency has been increased;

FIG. 9 illustrates an exemplary flow diagram for specifying settings toimplement an MEM strategy in a speech processing unit;

FIG. 10 illustrates an exemplary table of a default mapping thatprovides 12 effective filter channels;

FIG. 11 illustrates an exemplary table of a mapping after modificationby an audiologist;

FIG. 12 provides an alternative exemplary flow diagram for specifyingthe settings of a speech processing unit; and

FIG. 13 illustrates an exemplary mapping that includes mappings ofmultiple channels to groups of two or more electrically-coupledelectrodes.

DETAILED DESCRIPTION

The present invention is generally directed to a stimulating medicaldevice comprising a plurality of tissue-stimulating electrodes in whichthe electrode geometry may be adjusted without replacing or altering thephysical arrangement of the electrodes on or implanted in a recipient.An embodiment of the present invention includes a multi-electrodestimulating device that generates stimulation signals based on amultiple-to-one correspondence between filter channels and electrodes.This mapping of multiple filter channels to a single electrode, or asingle group of electrically-coupled electrodes, will be referred to asthe Multiple Electrode Mapping (MEM) strategy. In contrast to theone-to-one correspondence between filter channels and electrodes intraditional systems, the MEM strategy permits a mapping of two or morefilter channels to a single group of one or more electrodes.

The MEM strategy provides many advantages such as, for example, allowingelectrodes corresponding to different frequency ranges to be stimulatedat different stimulation rates to provide improved speech perception.For example, higher frequency channels may be stimulated at a higherrate to more closely approximate natural hearing. The MEM strategy alsoallows for combining frequency channels to provide effectively widerfrequency channels to individual electrodes, thus reducing the effectivenumber of frequency channels delivered to the electrodes of an electrodearray. Further assigning/delivering multiple filter channels to a singleelectrode (or a single group of electrically-coupled electrodes) that isstimulated at a higher stimulation rate has the effect of increasing thetemporal resolution of the system. Thus, combining multiple filterchannels may be used to shift a system from a system with a highspectral resolution (i.e., a large number of channels of stimulation)and low temporal resolution (i.e., a lower rate of stimulation) to asystem with lower spectral resolution (i.e., less stimulation channels)and higher temporal resolution (i.e., a higher rate of stimulation).

Embodiments of the present invention are described herein primarily inconnection with one type of stimulating medical device, a prosthetichearing implant system. Prosthetic hearing implant systems include butare not limited to hearing aids, auditory brain stimulators, andCochlear™ implants (also commonly referred to as Cochlear™ prostheses,Cochlear™ devices, Cochlear™ implant devices, and the like; generallyand collectively referred to as “cochlear implants” herein). Cochlearimplants use direct electrical stimulation of auditory nerve cells tobypass absent or defective hair cells that normally transduce acousticvibrations into neural activity. Such devices generally use an electrodearray inserted into the scala tympani of the cochlea so that theelectrodes may differentially activate auditory neurons that normallyencode differential pitches of sound. Auditory brain stimulators areused to treat a smaller number of recipients with bilateral degenerationthe auditory nerve. For such recipients, the auditory brain stimulatorprovides stimulation of the cochlear nucleus in the brainstem, typicallywith a planar electrode array; that is, an electrode array in which theelectrode contacts are disposed on a two dimensional surface that can bepositioned proximal to the brainstem. FIG. 1 is a perspective view of acochlear implant in which the effective width of the electrodes may beadjusted in accordance with the teachings of the present invention.

FIG. 1 is a perspective view of an exemplary cochlear implant system inwhich the present invention may be implemented. The relevant componentsof outer ear 101, middle ear 105 and inner ear 107 are described nextbelow. In a fully functional ear, outer ear 101 comprises an auricle 110and an ear canal 102. An acoustic pressure or sound wave 103 iscollected by auricle 110 and channeled into and through ear canal 102.Disposed across the distal end of ear cannel 102 is a tympanic membrane104 which vibrates in response to acoustic wave 103. This vibration iscoupled to oval window or fenestra ovalis 112 through three bones ofmiddle ear 105, collectively referred to as the ossicles 106 andcomprising the malleus 108, the incus 109 and the stapes 111. Bones 108,109 and 111 of middle ear 105 serve to filter and amplify acoustic wave103, causing oval window 112 to articulate, or vibrate. Such vibrationsets up waves of fluid motion within cochlea 116. Such fluid motion, inturn, activates tiny hair cells (not shown) that line the inside ofcochlea 116. Activation of the hair cells causes appropriate nerveimpulses to be transferred through the spiral ganglion cells (not shown)and auditory nerve 114 to the brain (not shown), where they areperceived as sound.

Cochlear implant system 100 comprises external component assembly 143which is directly or indirectly attached to the body of the recipient,and and internal component assembly 144 which is temporarily orpermanently implanted in the recipient. External assembly 143 typicallycomprises microphone 124 for detecting sound, a speech processing unit126, a power source (not shown), and an external transmitter unit 128.External transmitter unit 128 comprises an external coil 130 and,preferably, a magnet (not shown) secured directly or indirectly to theexternal coil. Speech processing unit 126 processes the output ofmicrophone 124 that is positioned, in the depicted embodiment, by ear110 of the recipient. Speech processing unit 126 generates codedsignals, referred to herein as a stimulation data signals, which areprovided to external transmitter unit 128 via a cable (not shown).Speech processing unit 126 is, in this illustration, constructed andarranged so that it can fit behind outer ear 110. Alternative versionsmay be worn on the body or it may be possible to provide a fullyimplantable system which incorporates the speech processor and/ormicrophone into the internal component assembly 144.

Internal components 144 comprise an internal receiver unit 132, astimulator unit 120 and an electrode assembly 118. Internal receiverunit 132 comprises an internal transcutaneous transfer coil (not shown),and preferably, a magnet (also not shown) fixed relative to the internalcoil. Internal receiver unit 132 and stimulator unit 120 arehermetically sealed within a biocompatible housing. The internal coilreceives power and data from external coil 130, as noted above. A cableor lead of electrode assembly 118 extends from stimulator unit 120 tocochlea 116 and terminates in an array 142 of electrodes. Signalsgenerated by stimulator unit 120 are applied by the electrodes ofelectrode array 142 to cochlear 116, thereby stimulating the auditorynerve 114.

In one embodiment, external coil 130 transmits electrical signals to theinternal coil via a radio frequency (RF) link. The internal coil istypically a wire antenna coil comprised of at least one and preferablymultiple turns of electrically insulated single-strand or multi-strandplatinum or gold wire. The electrical insulation of the internal coil isprovided by a flexible silicone molding (not shown). In use, internalreceiver unit 132 may be positioned in a recess of the temporal boneadjacent ear 110 of the recipient.

Further details of the above and other exemplary prosthetic hearingimplant systems in which embodiments of the present invention may beimplemented include, but are not limited to, those systems described inU.S. Pat. Nos. 4,532,930, 6,537,200, 6,565,503, 6,575,894 and 6,697,674,which are hereby incorporated by reference herein in their entireties.For example, while cochlear implant system 100 is described as havingexternal components, in alternative embodiments, implant system 100 maybe a totally implantable prosthesis. In one exemplary implementation,for example, speech processor 116, including the microphone, speechprocessor and/or power supply may be implemented as one or moreimplantable components. In one particular embodiment, speech processor116 may be contained within the hermetically sealed housing used forstimulator unit 126.

It should also be appreciated that although embodiments of the presentinvention are described herein in connection with prosthetic hearingdevice 100, the same or other embodiments of the present invention maybe implemented in other tissue-stimulating medical devices as well.Examples of such devices include, but are not limited to, other sensoryprosthetic devices, neural prosthetic devices, and functional electricalstimulation (FES) systems. In sensory prostheses, information iscollected by electronic sensors and delivered directly to the nervoussystem by electrical stimulation of pathways in or leading to the partsof the brain that normally process a given sensory modality. Neuralprostheses are clinical applications of neural control interfaceswhereby information is exchanged between neural and electronic circuits.FES devices are used to directly stimulate tissue having contractilecells to produce a controlled contraction of the same.

It should also be appreciated that although much of the description ofthe invention is directed to multiple channel-electrode mapping in whichadjacent filter channels are grouped and mapped together to stimulate asingle group of one or more electrodes, embodiments of the presentinvention are not limited to grouping adjacent channels, but rather maybe used to couple any desired filter channels of a simulating medicaldevice.

FIG. 2 is a high-level functional block diagram of one embodiment of acochlear implant system 100, referred to herein as cochlear implant 200.The functional blocks depicted in FIG. 2 are illustrative only. Thefunctions may be implemented in any combination of hardware, software orcombination thereof. The described functions and operations may becombined as depicted in FIG. 2 or may be combined or separated asdesired for a particular application.

Cochlear implant 200 comprises one or more microphone(s) 124 asdescribed above with reference to FIG. 1. It should be appreciated,however, that the any audio receiving device now or later developed maybe implemented in a prosthetic hearing implant also implementingembodiments of the present invention.

Microphone 124 provides a received audio signal to an audio preprocessor204. Audio pre-processor 204 may, for example, use a pre-emphasisfilter, a pre-amplifier, automatic gain control (AGC), an/or manualsensitivity control (MSC), and other signal pre-processing components.Audio-preprocessor 204 may be implemented, for example, in speechprocessing unit 126 described above with reference to FIG. 1. Thestructure and operation of audio-preprocessor 204 is considered to bewell-known in the art and, therefore, is not described further herein.Further details of exemplary embodiments of audio-preprocessor 204 maybe found in the US patents incorporated by reference elsewhere herein inthis application.

Audio pre-processor 204 provides output signals to filter bank 222,which preferably filters the received signals using a bank of band-passfilters 222 to obtain a plurality of frequency channel signals, eachcorresponding to a particular frequency band. For example, for animplant system providing up to 22 channels of stimulation, filter bank222 preferably has 22 separate band pass filters each providing afrequency channel signal corresponding a channel of stimulation. In thepresently discussed exemplary embodiments, two different exemplarytechnologies will be discussed for implementing filter bank 222. Thefirst technology is the Switched Capacitor Filter (SCF) technology thatuses a bank of switched capacitory filters (e.g., 22 separate band passfilters). This technology is a power-efficient hardware implementationthat enables a behind-the-ear (BTE) speech processor to be built. Thefilters of the SCF technology can be adjusted (scaled) in frequency bysimply changing a clock frequency of an internal clock. The SCFtechnology is currently implemented in the Spectra™ and ESPrit™ familyof speech processors for cochlear implant systems available fromCochlear, Inc. The second technology that will be discussed forimplementing filter bank 222 is the Digital Signal Processing (DSP)technology. This technology is implemented in software on a specialpurpose computer chip using various mathematical algorithms such as theFast Fourier Transform (FFT). DSP is a flexible technique that can beused to achieve better dynamic range than SCFs, but consumes more power.The DSP technology is currently implemented in the SPrint™ and Freedom™families of speech processors available from Cochlear, Inc. In systemsimplementing the DSP technology, the sound signals received bymicrophone 124 may be converted to digital signals prior to filteringby, for example, an Analog to Digital Converter (ADC)(not shown).

The filter channel signals are provided to an amplitude analysis andchannel selection block 224 (hereinafter “ACS block” 224) thatoptionally selects the maxima that will be used for stimulusapplication. ACS block 224 may also sample the received filter channelsignals to obtain energy estimates (amplitudes) of these signals attimes defined by a spectral analysis rate. Maxima selection andobtaining energy estimates of filter channel signals are well known tothose of ordinary skill in the art and, as such, are not describedfurther herein. For simplicity, the embodiments described herein will bepresented with reference to a Continuous Interleaved Sampling (CIS)system in which maxima are not selected, but instead all filter channelsare available for stimulation. A further description of an exemplary ACSblock is provided below.

The filter channels signals (or selected maxima of filter channelsignals) are then provided to a mapping and stimulation rate controllerblock 226 (hereinafter “M&SR block” 226) that preferably determines,based on the stimulation strategy being implemented, control informationfor use in applying stimulus via the electrode array 142, in accordancewith the received signals. For example, M&SR block 226 may select, foreach of the received filter channel signals (or maxima), theelectrode(s) to be used, the timing, the mode of stimulation and theamplitude of the stimulation to be applied. The selected mode ofstimulation may be, for example, bi-polar or mono-polar. In addition,electrodes may be electrically coupled to create electrode groups of oneor more electrodes. The electrodes may be grouped, for example, based ona pre-defined strategy for grouping the electrodes (e.g., a strategybased on testing of the implant system after implantation in an implantrecipient). Alternatively or additionally, the electrodes may bedynamically grouped based on, for example, characteristics of thereceived maxima or some combination of both predefined information anddynamic information. Various exemplary strategies for groupingelectrodes are described in further detail in related U.S. patentapplication Ser. No. 11/192,014, entitled “Variable Width ElectrodeScheme,” filed Jul. 29, 2005.

M&SR block 226 may also map one or more received filter channel signals(or maxima) to a single electrode or a single group of two or moreelectrodes. M&SR block 226 may map filter channels to electrodes basedon a map stored in SP configuration registers 230. This map may, forexample, map filter channels to electrodes in a one-to-onecorrespondence (i.e., a single filter channel is mapped to a singlecorresponding electrode), or a multi-to-one correspondence (i.e.,multiple filter channels are mapped to a single group of one or moreelectrodes). This map may be modifiable by an audiologist via SPprogramming interface 232. A further description of mapping multiplefilter channels to a single group of one or more electrically-coupledelectrodes is provided below.

The electrode information, timing information, mode of stimulation, andthe amplitude information may then be provided to a dataencoder/formatter 228, which encodes the information for transmissionover the trancsutaneous link to internal components 144. A myriad oftechniques may be implemented to effect the encoding of information fortransmission over the transcutaneous link (see, FIG. 1). These include,but are not limited to, sending information identifying table entries ofa table stored in stimulator unit 120, sending the raw information, etc.As one of ordinary skill in the art would appreciate, the implementedencoding technique depends on a variety of factors, including thespecific communication technique implemented. The encoded information,in this embodiment, is then provided to a power/data transmitter 242that transmits the signals using external coil 130. It should beappreciated that any communication technique now or later developed maybe implemented in embodiments of the presentation, including, forexample, via RF, IR percutaneous lead, etc. It should be appreciatedthat the structure and function of power/data transmitter 242 will beappropriate for the selected transmission technique.

An internal radio frequency (RF) receiver 246 receives the transmittedinformation via internal coil 244 and provides it to data encoder 248.Data encoder 248 then decodes the information. As one of ordinary skillin the art would appreciate, the decoding technique is preferably basedon the implemented encoding technique used by data encoder 228 and,accordingly, a myriad of different decoding techniques may beimplemented without departing from the invention.

The decoded information is then provided to stimulus output controllerand telemetry block 250 (hereinafter “SC&T block 250”) that uses thereceived information to direct the stimulation of the electrodes ofelectrode array 142. This may include, for example, generating timingand control signals for opening or closing electrode switches 252 forapplication of stimulus using electrode array 142. A further descriptionof exemplary techniques for opening and closing electrode switches 252to implement various stimulation schemes is provided U.S. patentapplication Ser. No. 11/192,014, entitled “Variable Width ElectrodeScheme,” filed Jul. 29, 2005.

As noted, speech processing unit 126 may also include a speech processor(SP) programming interface 232 through which an audiologist may connectto, for example, modify settings of the speech processing unit 126. Forexample, SP programming interface 126 may allow an audiologist toconnect speech processing unit 126 to a computer or other processorbased system. The audiologist may then access speech processing unit 126via diagnostic and programming user interface software 254 executing onthe computer to modify the settings of speech processing unit 126. Thesesettings may be stored, for example, in speech processing (SP)configuration registers 230. For example, the audiologist may use theuser interface 254 to modify the mappings of channels to electrodes,including the number and identity of filer channels mapped together, thegrouping of electrodes, the stimulation timing, the mode of stimulation,etc. A further description of an exemplary method for an audiologist tomodify the mapping of channels and electrodes is provided below.

Filter bank 222, ACS block 224, M&SR block 226, Data encoder formatter228, SP configuration registers 230 and SP programming interface 232 aredescribed herein as logical blocks of signal processing unit 126 and inpractice may be implemented in speech processing unit 116 of FIG. 1 by,for example, software, hardware, or any combination thereof.

FIG. 3 illustrates a more detailed diagram of one embodiment of filterbank 222, ASC block 224, and M&SR block 226. As illustrated, microphone124 may receive analog audio signals that are provided to audiopreprocessor 204, that among other things includes a preamplifier 322for amplifying the signals. Filter bank 222 may include a plurality ofband pass filters 302. As discussed above, two principle techniques maybe used for implementing filters 302: the SCF technique or the DSPtechnique. The band pass filtered signals are then provided to ASC block224, which may include envelope detectors 304 for detectinginstantaneous energy estimates (amplitudes) of the signal at thefrequency range corresponding to its corresponding band pass filter. ACSblock may also optionally include a maxima selector 306 for selecting anumber of maxima (i.e., the channels having the largest amplitude). Asis well known to those of skill in the art, various techniques may beused for selecting maxima. For example, in systems implementing theSpectral PEAK Extraction (SPEAK) or Advanced Combination Encoders (ACE)speech coding strategies employing an n of m scheme, a fixed number ofmaxima may be selected from the filter channels, such as for example,the 8, 16, etc. channels with the highest amplitude in a system with,for example, 22 filter channels. Or in other systems, such as a CISstrategy where all filter channels are used for stimulating electrodearray 142, a maximal selector 306 need not be used. For simplicity, theembodiments described herein will be described with reference to asystem in which maxima selector 306 is not used or turned off whenoperating in the MEM mode, and all filter channel signals are availablefor stimulating electrode array 142.

The filter channel signals (or selected maxima) are provided to MS&Rblock 226. As illustrated, this block may include a channel grouping,electrode allocation and stimulation sequence/arbitration block 308(hereinafter “CGAS block 308”), a stimulus mapping block 310(hereinafter, “SM block 310”), and a signal analysis rate andstimulation rate controller 312 (hereinafter “SR block 312”)

SR block 312 preferably provides stimulation rate information to CGASblock 308. This stimulation rate information, as discussed above, may bepreset by an audiologist. SR block 312 may also provide spectralanalysis rate information to ACS block 224. This spectral analysis rateinformation is used by ACS block 224 to control the rate at which energyestimates of each band are taken by envelope detectors 304 and the rateat which maxima are selected by optional maxima selector 306.Stimulation rates and spectral analysis rates are well known in the artand are not discussed further herein.

CGAS block 308 receives the filter channel signals (or selected maxima)and stimulation rate information and determines the signals forstimulating electrodes of electrode array 142. For example, CGAS block308 may provide SM block 310 with signals for the rate of stimulation,the group of electrodes to be stimulated, and the current amplitude forstimulating the electrodes. SM block 310 then maps the receivedinformation to the electrodes of electrode array 310. This mapping mayinclude amplitude mapping to generate a stimulus current level for eachstimulus to be applied along with generating the stimulus pulse timingsfor generating the pulses in accordance with the implemented strategy(e.g., timing for controlling the pulse widths, the interphase gaps,etc.). This mapping may also include mapping a single filter channel toa single group of one or more electrodes or mapping groups of 2 or morefilter channels to a single group of electrodes. In an exemplaryembodiment, CGAS block 308 may, for example, provide a group number(e.g., group 8) to SM block 310. SM block 310 then maps this groupnumber (e.g., group number 8) to the electrode(s) belonging to thisgroup (e.g., electrode 4). A further description of mapping a groupnumber to a group of one or more corresponding electrodes is providedbelow.

FIG. 4 depicts table 400, which illustrates an exemplary mapping forimplementing an MEM strategy in which multiple filter channels aremapped to a single group of one or more electrodes. As shown table 400includes a Group Number column 402, a Filter Channel Number column 404,and an Active Electrode column 406. The Filter Channel Number column 404identifies filter channels that are used in this exemplary embodiment.The Active Electrode column 406 identifies the active electrodes thatare assigned to the corresponding filter channel listed in FilterChannel Number column 404. As one of ordinary skill in the art is aware,active electrodes are electrodes that are “ON” and available forapplication of stimulus to an implant recipient. The Group Number column402 identifies a group to which the filter channel belongs. The groupnumber is used herein for illustrative purposes in describing groups inwhich multiple filter channels are assigned and in actualimplementations a group number need not be used.

As shown in table 400, in this exemplary MEM strategy, there are 8different groups of filter channels: 4 groups where a single filterchannel is mapped to a corresponding single electrode (i.e., groups1-4); 2 groups where 2 filter channels are mapped to a single electrode(i.e., groups 5 and 6); and 2 groups where 3 filter channels are mappedto a corresponding single electrode (i.e., groups 7 and 8). As such,this strategy will be referred to as a 1:1:1:1:2:2:3:3 strategy. In thisexample, 14 distinct filter channels are used. This table may be storedin SP configuration registers 230 where it may be modified by anaudiologist via SP programming interface 232. Further, this mappingtable may also be accessed by CGAS block 308 and SM block 310 toimplement the specified MEM strategy. Although table 400 illustrates anexample in which filter channels 9-22 are used and there are no gapsbetween these filter channels, other embodiments are possible where gapsexist. For example, in another embodiment, filter channel 22 may bemapped to electrode 22, filter channel 20 mapped to electrode 20, filterchannel 18 mapped to electrode 18, filter channel 16 mapped to electrode16, filter channels 13-14 mapped to electrode 14, filter channels 10-11mapped to electrode 10, filter channels 6-8 mapped to electrode 7, andfilter channels 2-4 mapped to electrode 4. As with the mapping of table400, this mapping also provides a 1:1:1:1:2:2:3:3 mapping strategy.

As discussed above, embodiments of the present invention may be used tovary the stimulation rate of signals applied at different frequencies.For example, embodiments may be used in which higher frequency channelsare mapped together so that they are stimulated at a higher frequency,as occurs in natural hearing. The following provides a more detaileddescription of exemplary mechanisms for implementing variablestimulation rates.

In typical systems employing the SPEAK or ACE strategies, thestimulation rate per channel provided by SR block 312 is determined froma preset value stored in SP configuration registers 230. CGAS block 308then receive the selected maxima and simply cycles through the selectedmaxima channels providing an electrode number and amplitude value to SMblock 310, which then stimulates corresponding electrodes at this fixedstimulation rate. Accordingly, in traditional systems, all electrodesare stimulated at an identical rate. For example, in a traditionalsystem employing an n of m strategy where n=8 and m=22, the systemselects 8 maxima from 22 filter channels. Each of these 8 maxima arethen applied at the same preset stimulation rate, which may, forexample, range from less than 800 pps to greater than 2000 pps.

In an embodiment employing the presently described Multiple ElectrodeMapping (MEM) strategy, CGAS block 308 receives the filter channelssignals (or selected maxima), and determines the corresponding timingthe electrode group corresponding to each received filter channel signal(or maxima) and other signals for stimulating electrodes of electrodearray 142. In its simplest form, CGAS block 308 receives the selectedmaxima and cycles through all channels (in this example, 14 filterchannels). FIG. 5 illustrates a table 500, which provides an exemplarystimulus timing sequence for such a simple stimulation strategy. Asillustrated, table 500 includes a Channel Group Number column 502 thatidentifies the channel group by its illustrative number along with thefilter channels assigned to this group number. Active Electrode column504 identifies the active electrodes assigned to the correspondingfilter channel group. Stimulus timing sequence columns 506 includes aplurality of time period columns 508. In this example, fourteen filterchannels are being used, and as such, fourteen time periods areavailable for application of stimulus. An X in a particular time periodcolumn 508 indicates that, in this example, stimulus for thecorresponding filter channels are applied during this time period.

The exemplary MEM strategy of table 500 results in bursts of stimulationon the electrodes to which multiple channels are mapped. For example, ifa stimulation rate of 800 pps per channel is used with the 14 differentchannels of table 500, the total stimulation rate is 11.2 kHz (i.e. 800Hz/channel * 14 channels). Thus, electrode 22, which corresponds tofilter channel 22, is stimulated at a rate of 800 Hz (i.e., it isstimulated once per frame of 14 pulses). Electrode 4, which is mapped inthis example to channel group 8 that includes 3 filter channels (filterchannels 2, 3, and 4), is stimulated 3 consecutive times (i.e., at timest1, t2, and t3) and then not stimulated again until the timing sequenceis repeated. Thus, electrode 4 is stimulated 3 times per 14 pulses, foran effective stimulation rate of 2400 Hz (3*800 Hz). This strategy,however, results in much higher burst rate for such a 3-channel to 1electrode allocation. That is, in this example, each pulse has a pulseduration of 89 microseconds (1/11.2 kHz). Thus, electrode 4 isstimulated a total of 3 times over a duration of 267 microsecond (3 * 89microseconds), or at a burst stimulation rate of 11.2 kHz (i.e., thetotal stimulation rate). Such a strategy may be acceptable forrelatively low stimulation rates of 800 pps or less.

For embodiments using a higher stimulation rate (e.g., of >2000 pps),the burst rate for the same situation (i.e., a 3-1 mapping) wouldbe >6000 pps. In such examples, it may be desirable to limit the maximumburst frequency to control temporal integration effects, in which casethe Stimulation Sequence Control function would cause all multiplechannel electrodes to be sequenced with all other electrodes to spreadout the stimuli that would otherwise be delivered as contiguous burst.FIG. 6 illustrates table 600, which provides such an alternative channeltiming sequence.

As shown in the exemplary timing sequence of table 600, electrode 4(mapped to channel group 8) is still stimulated at 3 times thestimulation rate of 800 pps (i.e., it is stimulated at an effectivestimulation rate of 2.4 kHz). But instead of channel 4 being stimulated3 consecutive times and having a burst rate equal to the totalstimulation rate (11.2 kHz), the stimulation of electrode 4 is spreadout over a longer time period. For example, in this embodiment,electrode 4 is stimulated 3 times over a period of 11 pulses, where eachpulse is 89 microseconds, for a total period of 981 microseconds. Thus,in this example, electrode 4 is stimulated at a burst rate of 3054 Hz (3pulses/981microseconds). These tables present exemplary mechanisms thatCGAS block 308 may utilize to stimulate electrodes according to theexemplary MEM strategy being discussed. It should be noted that numerousother strategies may be implemented for stimulating electrodes ofelectrode array 142 without departing from the invention. As will bediscussed in further detail below, the mapping of filter channels toelectrodes and the timing strategy for stimulating the electrodes may beset and modified by an audiologist using an external computer connectedto the speech processing unit 126 via SP programming interface 232.

In addition to be useful in enabling different frequency channels to bestimulated at different channel rates, embodiments of the MEM strategymay be used to reduce the number of effective filter channels and/or toeffectively modify the filter channels bandwidth. For example, ifmultiple filter channels are mapped to a single group of one or moreelectrodes, this has the effect of combining the multiple filterchannels into a single wider bandwidth filter channel that is stimulatedat a higher stimulation rate. As such, the MEM strategy may be used toconvert a system with a large number of filter channels that providehigh spectral selectivity and a predefined temporal resolution(determined by the available stimulation rate per channel) to a systemwith a smaller number of filter channels that provide reduced spectralresolution, but a greater temporal resolution via higher stimulationrates to the combined high frequency channels (in proportion to thenumber of channels that are combined. As discussed above, highertemporal resolution in the high frequency channels has been shown toimprove speech recognition.

As discussed above, band pass filter bank 222 is typically implementedvia either the SCF or DSP technologies. When using the SCF technology,the centre frequencies of the SCF filters can be shifted up or down bychanging the filter clock frequency. This has the effect of decreasingor increasing the useful audio frequency range (approximately 100 Hz to5,500 Hz) covered by the SCF band pass filters. FIG. 7 illustratesfilter bands for an exemplary SCF band pass filter bank. As shown, thisSCF filter bank has 20 bands in the 100 to 5,500 Hz range. These centerfrequency of these filter bands may then be increased or decreased byadjusting the filter clock frequency. For example, FIG. 8A depicts theeffect of decreasing the filter clock frequency, which is to shift thecenter frequency of the filters down, resulting in the same number ofchannels covering a lower range of frequencies. The center frequency ofthe filter bands may also be increased by, for example, increasing thefilter clock frequency. Shifting the filter clock frequency may also beused to reduce the number of filter channels in the useful audiofrequency range. FIG. 8B illustrates exemplary filter bands for the SCFband pass filter bank of FIG. 7, where the filter clock frequency hasbeen increased. As illustrated, FIG. 8A describes 12 bands in the 100 Hzto 5,500 Hz range. However, using such a system may result in the bandpass filters being shifted too high and low frequency information beinglost. For example, as shown if FIG. 8A, this system results in lowfrequency information below 800 Hz being lost. This may not bedesirable. An MEM strategy, such as described above, offers an improvedway to achieve a desired number of effective filter channels while stillbeing able to take advantage of the lower power consumption SCFtechnology. By using the MEM technology, multiple filter channels may becombined to achieve any desired number of effective filter channelswhile not losing low frequency information and

As discussed above, an audiologist may access the speech processor 126to modify its settings via SP programming interface 232. The followingprovides a more detailed explanation of two exemplary methods that maybe used for modifying the settings for a speech processing unit 126.Although two exemplary methods are provided below, it should be notedthat other methods may be used without departing from the invention.

FIG. 9 illustrates an exemplary flow diagram for specifying settings toimplement an MEM strategy in a speech processing unit. Initially, anaudiologist connects a computer or other device to speech processingunit 126 (S902). This may be achieved by, for example, connecting acable from the computer to the SP programming interface 232. Theaudiologist may then open a Diagnostic and Programming User Interfacesoftware program, such as program 254, that provides a user interfacefor modifying the settings of speech processing unit 126 (S904).Additionally, this software may communicate with speech processing unit126 to initially obtain information regarding the speech processing unitsuch as, for example, the number of filters channels of filter bank 222,the number of electrodes of electrode array 142, etc.

Using the user interface, the audiologist may then select the desiredspeech coding strategy (e.g., CIS, ACE, SPEAK) and the desired number ofeffective filter channels (S906). In this example, bandpass filters 222will be described as having 22 filter channels, electrode array 142 has22 electrodes, and the user selects the CIS strategy and 12 effectivefilter channels. Using this information, the software then creates adefault channel map that it then presents to the audiologist (S908).This default map may be, for example, a 22 channel map with 10 of the 22channels disabled (i.e., unused) and 12 of the channels mapped to acorresponding single electrode in a 1:1 correspondence. This may beaccomplished, by for example, using an SCF scheme, such as illustratedin FIG. 8B. FIG. 10 illustrates table 1000, which provides an exemplarytable of a default mapping that provides 12 effective filter channels.As illustrated, table 1000 includes a Filter Channel Number column 1002,a used/unused column 1004, an Electrode column 1006, and anActive/Inactive column 1008. The Used/Unused column 1004 indicateswhether the corresponding filter channel is being used in this scheme,where a “1” indicates it is in use, and a “0” indicates that it is notused. The Active/Inactive column 1008 indicates whether thecorresponding electrode identified in electrode column 1006 is active orinactive (i.e., is to be used or not), where “1” indicates that theelectrode is active and “0” indicates that it is inactive. Arrows 1010are used to illustrate the mapping of filter channels to electrodes. Forexample, as shown, filter channel 22 is mapped to electrode 22, filterchannel 21 is mapped to electrode 21, filter channel 20 is mapped toelectrode 19, filter channel 19 is mapped to electrode 18, filterchannel 18 is mapped to electrode 16, filter channel 17 is mapped toelectrode 14, filter channel 16 is mapped to electrode 12, filterchannel 15 is mapped to electrode 10, filter channel 14 is mapped toelectrode 8, filter channel 13 is mapped to electrode 6, filter channel12 is mapped to electrode 4, and filter channel 11 is mapped toelectrode 2. In an alternative embodiment, the 12 selected channels maybe evenly spaced over the 22 filter channels using, for example, a bandpass filter scheme such as illustrated in FIG. 7. For example, in suchan alternative embodiment, filter channels, 22, 20, 18, 16, 14, 12, 10,8, 6, 4, 2, and 1 may be used where each is mapped to a singlecorresponding electrode in a 1:1 fashion (i.e., the filter channels aremapped to electrodes 22, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, and 1,respectively).

This default table may then be modified by the audiologist (S910). Thismay be accomplished by the audiologist, for example, clicking on theentries they wish to modify and manually modifying the entries. Forexample, the audiologist may click on a filter channel that brings up awindow that allows the audiologist to specify to which electrode thefilter channel is mapped. It should be noted that this is but oneexample and numerous mechanisms are possible for permitting anaudiologist to specify mappings without departing from the invention.Additionally, the software may include a validation function to ensurethat the audiologist's entries are correct and notify the audiologist ofany incorrect entries, thus allowing the audiologist to correct any sucherrors.

FIG. 11 illustrates table 1100, which provides an exemplary table of amapping after modification by an audiologist of the mapping of table1000 that provides 12 effective filter channels mapped to 8 electrodes.Circles 1112 indicate the groupings of filter channels. This mappingincludes mappings of multiple filter channels to a single group of oneor more electrodes. For example, as illustrated filter channel 22 ismapped to electrode 22, filter channel 21 is mapped to electrode 20,filter channel 20 is mapped to electrode 18, filter channel 19 is mappedto electrode 16, filter channel 18 is mapped to electrode 14, filterchannels 16 and 17 are mapped to electrode 10, filter channels 14 and 15are mapped to electrode 7 and filter channels 11, 12, and 13 are mappedto electrode 4. Although in this example, all used filter channels areadjacent, in other examples they need not be adjacent and gaps may existbetween used filter channels.

This exemplary mapping strategy maps 12 filter channels to 8 differentelectrodes in a 1:1:1:1:1:2:2:3 manner (i.e., 5 groups where 1 filterchannel is mapped to 1 electrode; 2 groups where 2 filter channels aremapped to 1 electrode, and 1 group where 3 electrodes are mapped to asingle electrode). In an alternative embodiment, such as the alternativeto table 1000 discussed above, the audiologist may specify a mappingscheme in which gaps in the filter channels exist. For example, theaudiologist may specify a mapping scheme in which filter channel 22 ismapped to electrode 22, filter channel 19 is mapped to electrode 19,filter channel 16 is mapped to electrode 16, filter channel 14 is mappedto electrode 14, filter channel 12 is mapped to electrode 12, filterchannels 9 and 10 are mapped to electrode 10, filter channels 6 and 7are mapped to electrode 7, and filter channels 2, 3, and 4 are mapped toelectrode 4.

After the audiologist modifies the mappings, the audiologist may thenperform psychophysics on the selected electrodes to determine thethreshold and maximum comfort levels for each of the selected electrodes(S912). This information may then be stored in SP configurationregisters 230 for use by the signal processing unit (S914). It should benoted that table 1100 provides one exemplary mapping and other mappingsmay be used, such as the mapping illustrated in table 400, withoutdeparting from the invention.

FIG. 12 provides an alternative exemplary flow diagram for specifyingthe settings of a speech processing unit. As with the flow of FIG. 9,the audiologist first connects a computer, or other device, to thespeech processing unit 126 (S1 202) and opens Diagnostic and Programminguser interface software 254 for modifying the settings of the speechprocessing unit 126 (S1204). The audiologist may then select toimplement an MEM strategy (S1206). For example, an audiologist may clickon a “Multiratio CIS“ coil displayed in a user interface to beginimplementing an MEM strategy, may click on an appropriate toolbar, ormay select to implement the MEM strategy by any other appropriate means.The audiologist may then be prompted to enter the number of electrodesthey desire to set as active (e.g., 12) along with the total desiredfrequency range for the filter bank 222 (e.g., 800 Hz to 10 kHz). Thesoftware may then automatically select the electrodes to use and displaythe selected electrodes to the user (S1208). This default selection ofelectrodes may, for example, be such that the selected electrodes areevenly spaced across the selected frequency range, such as the selectedelectrodes illustrated in table 1000.

The audiologist may then modify the selected electrodes (S1210). Thismay be accomplished by the audiologist clicking on the entries in adisplayed table and manually selecting electrodes as either active orinactive. Once the electrodes are selected, the software may thenautomatically allocate stimulation rate integer ratios for eachelectrode based on default lookup tables that may be stored by thesoftware and modifiable by the audiologist (S1212). For example, thisdefault lookup table may store information indicating higher frequencyelectrodes are to be stimulated at a higher rate than lower frequencyelectrodes. For example, the table may store integer values indicatingthat high frequency electrodes are to be stimulated at a rate threetimes greater than low frequency electrodes, and mid frequencyelectrodes are to be stimulated at a rate twice that of low frequencyelectrodes. These selected stimulation rate ratios are then used by thesoftware to determine the number of filter channels to be mapped to eachof the selected electrodes. For example, a given map may use ratios of1:1:1:1:2:2:3:3, such as the map of table 400 or, for example, ratios of1:1:1:1:1:2:2:3, such as the map of table 1100. These ratios maybestored in the default look up tables. Additionally, the software mayalso automatically divide the frequency range among the channels using,for example, default look up tables.

The selected mapping table may then be presented to the audiologist, whomay manually modify the settings if desired (S1214). After which, theaudiologist may then perform standard psychophysics on the selectedelectrode to set the threshold and maximum comfort level of each of theselected electrodes (S1216). This information may then be stored in SPconfiguration registers 230 for use by the speech processing unit 126(S1218).

Further, in addition to specifying the mapping of the filter channels toelectrodes, the software may also permit the audiologist to specify thestrategy for stimulating the electrodes. For example, the audiologistmay be presented with a default stimulation strategy, such asillustrated in Tables 500 and/or 600. The user may then select tomanually modify the table to effect a different stimulation strategy.Additionally, the software may permit the audiologist to enterparameters that the software will use in creating the defaultstimulation strategy. For example, the audiologist may be able tospecify that the maximum burst rate for any particular mapping notexceed a particular value, such as, for example, 4000 Hz or a fractionof the total stimulation rate (e.g.,⅛^(th) the total stimulation rate or2700 Hz for a system with a total stimulation rate of 21.6 kHz). Or, forexample, the software may by default generate a stimulation strategythat minimizes the maximum burst rate as much as possible. The softwaremay also permit the audiologist to specify other settings for use by thesystem, such as the stimulation rate for each channel (e.g., 800 pps),the spectral analysis rate, etc.

Although the above-discussed embodiments were discussed with referenceto the CIS speech encoding strategy, other speech coding strategies maybe used when converting sound into an electrical stimulation signals.For example, embodiments of the present invention may be used incombination with a variety of speech strategies including but notlimited to Continuous Interleaved Sampling (CIS), Spectral PEAKExtraction (SPEAK), Advanced Combination Encoders (ACE), SimultaneousAnalog Stimulation (SAS), MPS, Paired Pulsatile Sampler (PPS), QuadruplePulsatile Sampler (QPS), Hybrid Analog Pulsatile (HAPs), n-of-m andHiRe™, developed by Advanced Bionics. SPEAK is a low rate strategy thatmay operate within the 250-500 Hz range. ACE is a combination of CIS andSPEAK. Examples of such speech strategies are described in U.S. Pat. No.5,271,397, the entire contents and disclosures of which is herebyincorporated by reference. The present invention may also be used withother speech coding strategies, such as a low rate strategy calledSpread of Excitation which is described in U.S. Provisional No.60/557,675 entitled, “Spread Excitation and MP3 coding Number fromCompass UE” filed on Mar. 31, 2004, U.S. Provisional No. 60/616,216entitled, “Spread of Excitation And Compressed Audible Speech Coding”filed on Oct. 7, 2004, and PCT Application WO 02/17679A1, entitled“Power Efficient Electrical Stimulation,” which are hereby incorporatedby reference herein.

Further, although the above-discussed embodiment were discussed withreference to mapping groups of filter channels to a single electrode, inother embodiments electrodes may be electrically coupled to form anelectrode group comprising two or more electrodes. For example, in anembodiment any desired combination of two-or more electrodes may beelectrically-coupled to each other so that a stimulating signal may besimultaneously applied to or generated on (generally referred to as“applied to”) the electrically coupled electrodes via a single source,such as a single current source. When implemented in a prosthetichearing implant system, the group(s) of electrically-coupled electrodesmay each be managed as a single electrodes along with any individualelectrodes. That is, the electrode groups and single electrodes may becontrolled to simultaneously or sequentially apply stimulating signal tothe cochler in accordance with a selected stimulation strategy.

Altering the electrode geometry by electrically coupling electrodesprovides many advantages. Take, for example, systems in which theelectrodes are arranged in a linear, array, as is commonly utilized in aprosthetic hearing implant. Electrically coupling and/or de-coupling twoor more adjacent or proximate electrodes of the array changes theeffective electrode surface area through which a stimulating signal isapplied to the auditory nerves of a cochlear. Adjusting the effectivewidth of electrodes allows for the dynamic control of the spread ofexcitation by altering the region of neural excitation. In addition, theeffective electrode width may be adjusted to adapt the electrode arrayto a cochlea having a particular pattern of functional auditory nerves.

A further advantage in the above or other applications is thatelectrically coupling two or more electrodes reduces electrodeimpedance. Because power consumption typically increases with increasingstimulus current, a reduction in electrode impedance reduces the powerconsumption of the implant system. This is particularly advantageouswhen used in conjunction with high-density electrode arrays. The designof intra-cochlea electrode arrays has been driven by the need to achievea higher density of discrete electrodes positioned closer to the innerwall of the cochlea (or modiolus) with the objective of increasingspectral resolution and reducing stimulation thresholds. As the densityof an electrode array increases (density being defined by the number ofelectrodes per unit length of the array), the electrode area becomessmaller, resulting in an increased impedance. By electrically couplingtwo or more electrodes, the impedance of the electrode array may bereduced. A further description of methods and systems forelectrically-coupling electrodes to form groups of electrodes isprovided in the above-incorporated by reference U.S. patent applicationSer. No. 11/192,014, entitled “Variable Width Electrode Scheme,” filedJul. 29, 2005.

FIG. 13 illustrates table 1300, which provides an exemplary mapping thatincludes mappings of multiple channels to groups of two or moreelectrically-coupled electrodes. For example, as shown, group 1consisting of filter channel 22 is mapped to three electrodes(electrodes 20, 21, and 22), group 2 consisting of filter channel 19 ismapped to electrodes 18 and 19, group 3 consisting of filter channel 15is mapped to electrodes 15, 16, and 17, group 4 consisting of electrode14 is mapped to electrode 14, group 5 consisting of filter channels 12and 13 is mapped to electrodes 12 and 13, group 6 consisting of filterchannels 10 and 11 is mapped to electrode 10, group 7 consisting offilter channels 6, 7, and 8 is mapped to electrode 7, and group 8consisting of filter channels 2, 3, and 4 is mapped to electrodes 3 and4.

It should be noted that table 1300 merely illustrates on exemplary wayin which multiple filter channels may be mapped to groups of one or moreelectrodes. For example, in table 1300, there are gaps between filterchannels (e.g., filter channel 21 is not used). In other embodiments, itmay not be desirable to have gaps. In such an example, adjacent filterchannels may be used and a scheme such as illustrated in FIG. 8B may beused to reduce the number of used filter channels. Numerous othermappings are possible without departing from the invention.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

All documents, patents, journal articles and other materials cited inthe present application are hereby incorporated by reference. Althoughthe present invention has been fully described in conjunction withseveral embodiments thereof with reference to the accompanying drawings,it is to be understood that various changes and modifications may beapparent to those skilled in the art. Such changes and modifications areto be understood as included within the scope of the present inventionas defined by the appended claims, unless they depart therefrom.

1-19. (canceled)
 20. A method for delivering a stimulating signal by astimulating medical device having a plurality of electrodes, comprising:receiving a signal; filtering the received signal to obtain a pluralityof band pass filtered signals; delivering to each electrode of a firstgroup of one or more electrodes, a first set of stimulation signals,wherein the first set of stimulation signals comprises stimulationsignals for each of a first filter channel group of two or more bandpass filtered signals; and delivering to each of electrodes of a secondgroup of one or more electrodes, a second set of stimulation signals,wherein the second set of stimulation signals comprises stimulationsignals for each of a second filter channel group of one or more bandpass filtered signals; and wherein the first set of stimulation signalsare delivered at a different effective stimulation rate than the secondset of stimulation signals.
 21. The method of claim 20, wherein the bandpass filtered signals of the first filter channel group comprise higherfrequency signals than the band pass filtered signals of the secondfilter channel group; and wherein the first set of stimulation signalsare delivered at a higher effective stimulation rate than the second setof stimulation signals.
 22. The method of claim 21, wherein the firstfilter channel group are mapped to a first group of one or moreelectrodes and the second filter channel group are mapped to a secondgroup of one or more electrodes, and wherein the mapping is performed bysoftware that automatically maps higher frequency filter channel groupsto more band pass filters than lower frequency channel groups.
 23. Themethod of claim 20, wherein the delivering of the first set ofstimulation signals, comprises delivering the signals of the first setof stimulation signals interspaced with other stimulation signals inorder to reduce a burst rate for the delivering of the first set ofstimulation signals.
 24. The method of claim 23, wherein the deliveringof the first set of stimulation signals comprises automatically limitingthe burst rate for delivering the first set of stimulation signals. 25.The method of claim 20, wherein the first group of electrodes comprisestwo or more electrodes, the method further comprising: electricallycoupling the electrodes comprising the first group of electrodes; andwherein the delivering of the first set of stimulation signals comprisessimultaneously delivering to the group of electrically-coupledelectrodes a stimulation signal from the first set of stimulationssignals.
 26. The method of claim 25, wherein the simultaneous deliveringof the stimulation signal to the first group of electrodes comprises:simultaneously delivering the stimulation signal to the first group ofelectrically-coupled electrodes a stimulation signal via a singlecurrent source.
 27. A cochlear implant system, comprising: a pluralityof electrodes disposed in a cochlear of a recipient, wherein theplurality of electrodes comprise a first group of one or more electrodesand a second group of one or more electrodes; a speech processing unitcomprising a plurality of band pass filters configured to processreceived acoustical signals to obtain a plurality of band pass filteredsignals; and a stimulator unit configured to deliver to each electrodeof a first group of one or more electrodes, a first set of stimulationsignals, wherein the first set of stimulation signals comprisesstimulation signals for each of a first filter channel group of two ormore band pass filtered signals, and to deliver to a second group of oneor more electrodes a second set of stimulation signals, wherein thesecond set of stimulation signals comprises stimulations signals foreach of a second filter channel group of one or more band pass filteredsignals, and wherein the first set of stimulation signals are deliveredat a different effective stimulation rate than the second set ofstimulation signals.
 28. The system of claim 27, wherein the speechprocessing unit further comprises: a processor configured to map thefirst filter channel group of two or more band pass filtered signals tothe first group of one or more electrodes, and to map the second filterchannel group of one or more of the band pass filtered signals to thesecond group of one or more electrodes; and wherein the band passfiltered signals of the first filter channel group comprise higherfrequency signals than the band pass filtered signals of the secondfilter channel group; and wherein the first set of stimulation signalsare delivered at a higher effective stimulation rate than the second setof stimulation signals.
 29. The system of claim 28, wherein theprocessor comprises software configured to map the first filter channelgroup to the first group of one or more electrodes and map the secondfilter channel group to the second group of one or more electrodes, andwherein the software automatically maps higher frequency filter channelgroups to more band pass filters than lower frequency channel groups.30. The system of claim 27, wherein the speech processing unit isconfigured to direct the stimulator unit to deliver the signals of thefirst set of stimulation signals interspaced with other stimulationsignals in order to reduce a burst rate for the delivering of the firstset of stimulation signals.
 31. The system of claim 30, wherein thespeech processing unit comprises software configured to automaticallylimit the burst rate for delivering the first set of stimulationsignals.
 32. The system of claim 27, wherein the first group ofelectrodes comprises two or more electrodes, and wherein the stimulatorunit is configured to electrically couple the electrodes comprising thefirst group of electrodes, and to simultaneously deliver a stimulationsignal to the first group of electrically-coupled electrodes.
 33. Thesystem of claim 32, wherein the stimulator unit is further configured tosimultaneously deliver the stimulation signal to the first group ofelectrically-coupled electrodes via a single current source.
 34. Asystem for delivering a stimulating signal by a stimulating medicaldevice having a plurality of electrodes, comprising: means for receivinga signal; means for filtering the received signal to obtain a pluralityof band pass filtered signals; means for delivering to each electrode ofa first group of one or more electrodes, a first set of stimulationsignals, wherein the first set of stimulation signals comprisesstimulation signals for each of a first filter channel group of two ormore band pass filtered signals; and means for delivering to each ofelectrodes of a second filter channel group of one or more electrodes, asecond set of stimulation signals, wherein the second set of stimulationsignals comprises stimulations signals for each of a second group of oneor more band pass filtered signals; and wherein the first set ofstimulation signals are delivered at a different effective stimulationrate than the second set of stimulation signals.
 35. The system of claim34, wherein the band pass filtered signals of the first filter channelgroup comprise higher frequency signals than the band pass filteredsignals of the second filter channel group; and wherein the first set ofstimulation signals are delivered at a higher effective stimulation ratethan the second set of stimulation signals.
 36. The system of claim 35,wherein the first filter channel group are mapped to a first group ofone or more electrodes and the second filter channel group are mapped toa second group of one or more electrodes, and wherein the mapping isperformed by software that automatically maps higher frequency filterchannel groups to more band pass filters than lower frequency channelgroups.
 37. The system of claim 37, wherein the first group ofelectrodes comprises two or more electrodes, the system furthercomprising: means for electrically coupling the electrodes comprisingthe first group of electrodes; and wherein the means for delivering ofthe first set of stimulation signals comprises means for simultaneouslydelivering to the group of electrically-coupled electrodes a stimulationsignal from the first set of stimulation signals.